The original adduser/rmuser scripts in Perl used to modify the PATH

The original adduser/rmuser scripts in Perl used to modify the PATH
setting.  When the scripts were converted to Bourne shell, this was
removed.  The adduser script was changed to use an explicit path for
the pw(8) command so that /usr/sbin did not have to be in the user's
PATH.  The rmuser script continued to assume that /usr/sbin was in the
user's path, however.  This fixes the rmuser script to use an explicit
path for pw(8) similar to adduser.

MFC after:	2 weeks